(I just ordered the HD-558s last night and the cans should be arriving on Monday.)
People can post comparisons of their HD-558 verses other headphones (and other Sennheisers) they use.
Post Ideas for any modds for the HD-558.
Find out which Headphone Amplifers bring out the best of the HD-558s.
Figure out which EQ settings bring out the best for movies, music, games, etc.
So just anything to do with the HD-558s.